1. Field of the Invention
The present invention relates to a semiconductor pressure sensor and, more specifically, to a semiconductor pressure sensor composed of a pressure sensitive element formed by anodic bonding and used in automobiles and the like.
2. Description of the Related Art
FIG. 5 is a cross sectional view showing a conventional semiconductor pressure sensor. In FIG. 5, a pressure sensing element 4 is composed of a pressure sensor chip 2 which has a diaphragm 1 and is anodically bonded to a glass base 3. The pressure sensing element 4 is die bonded to a sunk die pad 5a by a bonding resin 6. Further, the pressure sensor chip 2 is electrically connected to an outer lead 7 through a metal wire 8.
The sunk die pad 5a and the outer lead 7 are integrally formed as a lead frame in a manufacturing process. A pressure sensor element 12 is formed in such a manner that the lead frame is fixed by, for example, a bonding resin 11, such as an epoxy resin or the, like and held between a package cover and a package base 10 and the frame of the lead frame is cut off. The pressure sensor element 12 is mounted on a thick film substrate 13 with a lead wire such as, for example, a ceramic substrate or a hybrid IC substrate by the outer lead 7 through solder 14 to make a semiconductor pressure sensor 15.
The conventional semiconductor pressure sensor 15 is arranged as described above and the diaphragm 1 of the pressure sensor chip 2 includes a vacuum chamber produced by anodically bonding the pressure sensor chip 2 to the glass base 3 in a vacuum. The vacuum serves as a reference pressure. When an external pressure is applied to the surface of the pressure sensor chip 2 through the opening of the package cover 9, an output signal is produced in accordance with the external pressure by a bridge circuit of gauge resistors (not shown). The diaphragm 1 formed by a thin wall is strained and the gauge resistors on the surface of the pressure sensor chip 2 are changed in resistance by a piezoresistance effect. The thus-produced output signal is sensed through the outer lead 7 and the metal wire 8.
In the aforesaid semiconductor pressure sensor, when the die pad is sunk, the sunk die pad 5a may not be in contact with the package base 10 because the amount of sinking of the die pad 5a varies. Since the sunk die pad 5a is fixed to the package base 10 only on the one side thereof by hanging leads 16 as shown in FIG. 6, there is a problem in that the pressure sensing element 4 is displaced by vibrations and the like and the metal wire 8 may be broken and the electrical signal of the pressure sensor chip 2 disrupted.
Further, there is also a problem that since the die pad is sunk, the size of a package is increased and processing is difficult.